Infrared (IR) systems have been widely used in the past. A conventional system has an array of large-area detectors wherein each detector corresponds to a single picture element (pixel) for an image. Each detector is a planar structure that has both the length and width dimensions larger than the wavelength of the incident radiation such that the detector has adequate collection area for the incident radiation.
A principal limitation has been the spectral or polarization response of infrared systems. Typically, an infrared detector is responsive to only a small region of infrared radiation or to the entire band of infrared radiation. Systems for multi-spectral or multi-polarization response use multiple detectors, sensitive to different wavelengths or different polarizations of infrared radiation, together with a beamsplitter to direct the infrared radiation to the multiple detectors.
Current systems for polarization control generally require bulk optical systems having multiple moving parts. Image forming radiation is typically collected for a fixed polarization state. Optical filters must be used in the optical train before the receiving detector array. The selection of the polarization state requires mechanical motion of the optical filters. The typical weight of the necessary filter and switching assemblies is on the order of 1 kg or more. The required time to switch between polarization states can be on the order of 2 seconds or more. Polarization-resolved imagery is largely unexploited, because of inconvenient implementation.
Multi-spectral and multi-polarization infrared response is alternatively achieved by integrating spectral or polarization filters onto each pixel of a detector or by fabrication of adjacent pixels with materials of different bandgaps.
Many U.S. patents have been proposed for infrared detectors but have many of the problems previously described including the preference inadequacy of the antenna systems. Arrays of infrared sensors are known: see for example U.S. Pat. No. 5,021,663 to Hornbeck; U.S. Pat. No. 5,286,976 to Cole; U.S. Pat. No. 5,300,915 to Higashi, et al; U.S. Pat. No. 5,367,167 to Keenan; U.S. Pat. No. 5,591,959 to Cigna, et al; U.S. Pat. No. 5,647,956 to Belcher, et al; and, U.S. Pat. No. 5,436,453 to Chang et al but nowhere is there a mention of antenna-coupled sensors.
Blackwell, et al in U.S. Pat. No. 5,760,398 mentions an antenna (see col. 4, lines 18 and 67; col. 20, line 64 and col. 22, line 1) with respect to absorption of incident radiation but only in reference to the primary focus of their disclosure, i.e., the area receiver pixel radiation collector which is geometrical optical based.
Gooch in U.S. Pat. No. 5,777,328 discloses bolometer arrays with no antennas and each bolometer “a separately sensed pixel” (see col. 15, line 32).
Silver, et al in U.S. Pat. No. 5,777,336 discloses an array of microcalorimeters responsive to x-ray fluorescence, not infrared radiation.
Jack et al. in U.S. Pat. No. 6,329,655 discloses an improved coupling of the antenna to the detector element.
Choi in U.S. Pat. No. 6,410,917 discloses a polarization sensitive quantum well infrared photodetector (QWIP) where the detector unit is formed by a group of C-QWIP detectors having different groove orientations (see col. 3, line 22).
Grinberg et al. in U.S. Pat. No. 6,441,368 discloses an array of bolometers responsive to millimeter wave radiation, not infrared radiation.
Baker in U.S. Pat. No. 5,239,179 discloses an infrared detector device responsive to more than one wavelength of infrared radiation. The infrared detector elements are formed on the lower and upper levels of material of the substrate with the elements on the lower level having an infrared response different from the elements formed on the upper level.
Thus, the need exists for solutions to the problems in the prior art described above.